Kohl's, Land's End, and Sam's Club are among the brands going out early.

In the process, they're effectively bringing the seven-year tradition of Cyber Monday to an end.

“Cyber Monday is passé," Fiona Dias tells us.

Dias, the chief strategy officer of ShopRunner, a membership program that offers Amazon Prime-like two-day delivery for a number of retailers, is the former chief marketing officer of Circuit City, so she has firsthand experience with the Cyber Monday phenomenon.

Retailers who don't jump the gun are "missing out on a bonus day of purchases," and risking losing customers who spend their holiday budgets early, Dias added.

Cyber Monday began in 2005, giving a name to the phenomenon that online retailers saw at the time: American shoppers who spent the long weekend after Thanksgiving in stores returned to work on Monday and used high-speed Internet connections at the office to keep buying.

But that scenario posited that a desktop PC with a broadband connection was the best way to shop. And the fast-moving tech world has upended those assumptions.

Even as Cyber Monday blossomed, the seeds of its downfall had been planted. Broadband penetration in homes with computers continued to soar, hitting 90 percent this year. The iPhone came in 2007, with the iPad following in 2010, providing mobile buying experiences that didn't try shoppers' patience.

And employers seem to be losing patience with the practice: 7 percent of HR managers surveyed by PayScale said last year that they'd fired an employee for shopping at work.

With most stores closed on Thanksgiving, it's easy to see the holiday given over to online shopping—likely on a tablet, while the rest of the family watches football.

Online retailers we've spoken to, like Fab and One Kings Lane, report that mobile sales now make up anywhere from 25 to 40 percent of sales.

With customers ready to shop at any time on tablets and smartphones, why make them wait for Monday?

The simple answer is tradition. Retailers have trained customers to look for online deals on the Monday after Thanksgiving, a self-reinforcing expectation. Adobe, whose software tracks website activity across 500 large retailers, predicts that Cyber Monday sales will hit $2 billion this year.

Like Black Friday, the casually observed retail phenomenon turned into an institutionalized event, Cyber Monday may well outlive its usefulness.